Rethinking Disorders of Consciousness: New Research and Its Implications
- Rethinking Disorders of Consciousness:New Research and Its Implications
Over the past several years, deciding whether to withdraw life-sustaining therapy from patients who have sustained severe brain injuries has become much more difficult. The problem is not the religious fundamentalism that infused the debate over the care of Terry Schiavo, the Florida woman in a permanent vegetative state whose case has drawn national attention. Rather, the difficulty stems from emerging knowledge about the diagnosis and physiology of brain injury and recovery. The advent of more sophisticated neuroimaging techniques like MRI and PET scans, in tandem with electrophysiologic and observational studies of brain-injured patients, have led to an effort to differentiate disorders of consciousness more precisely. The crude categories that have informed clinical practice for a quarter century are becoming obsolete.
It used to be enough for a neurologist or neurosurgeon to write a note in the chart grimly recording the patient's neurological exam and then concluding with the global statement, "no hope for meaningful recovery." It can no longer be so simple. With a better understanding of brain injury and mechanisms of recovery, we should be suspicious of blanket statements that might, we now believe, obscure important differences among different patients' prospects for recovery, although even those patients we now think may recover may still be left with profound and perhaps intolerable burdens of disability.
Recovery from coma depends on a patient's age, the site of injury, and whether the damage was done by trauma, anoxia (oxygen deprivation), or other processes. The most severe brain injuries may lead to brain death. If patients survive and begin to recover from coma, they often first enter into the vegetative state, first described by Bryan Jennett and my teacher, Fred Plum, in 1972. The vegetative state is a paradoxical state of "wakeful unresponsiveness" in which the eyes are open but there is no awareness of self or environment. When a vegetative state continues beyond thirty days, it is described as "persistent." A vegetative state is generally considered permanent three months after anoxic injury and twelve months after trauma.
All of this is news since I went to medical school. I was taught that the vegetative state was immutable and fixed. Vegetative brains were, if I recall the phrase correctly, "gelatinous gels." The futility of this brain state was the basis for the establishment of the right to die in cases like Quinlan and Cruzan. Recent studies have shown, however, that patients can regain some evidence of consciousness before the vegetative state becomes permanent. In the window between the persistent and permanent vegetative state, patients can progress to what has been described as the "minimally conscious state" (MCS). Unlike vegetative patients, the minimally conscious demonstrate unequivocal, but fluctuating, evidence of awareness of self and the environment. The natural history of MCS patients is not yet known. Near the upper boundary of this category, patients may say words or phrases and gesture. They also may show evidence of memory, attention, and intention. Patients are considered to have "emerged" from MCS only when they can reliably and consistently communicate.
Unfortunately, all of this is easier to explain in theory than to observe in practice. First and foremost is the challenge of diagnosis. To the untrained eye, MCS patients may appear very similar to those who are vegetative. These diagnoses can be confused and conflated and in the earlier phases of illness need to be considered very carefully in the context of the mechanism of injury. In a patient with non-anoxic injury, even small gains beyond the vegetative level may herald the potential for significant further recovery. Some recent studies suggest that the diagnostic distinction between MCS and PVS is missed by neurologists at rates that would be intolerable in other clinical domains. To be fair, however, a neurologist acting in good faith might examine an MCS patient when his level of arousal was low and elicit an exam that is indistinguishable from a vegetative patient.
But there is another sort of diagnostic error that occurs when the objectivity of diagnosis is infiltrated by value judgments. Instead of dealing with the moral ambiguity associated with balancing the burdens...
